Frequency-tunable light sources and methods of generating frequency-tunable light

Abstract

Frequency-tunable light sources and methods of generating frequency-tunable light are described. In one aspect, a frequency-tunable light source includes a resonant optical cavity, an optical gain medium, an optical mode filter, and a mode frequency tuner. The resonant optical cavity supports oscillation of light in at least one longitudinal mode having a respective mode frequency. The optical gain medium is disposed in the resonant optical cavity and is operable to amplify light. The optical mode filter is arranged to intercept light oscillating in the resonant optical cavity and has an optical transmission pass-band with a tunable center frequency. The mode frequency tuner is arranged to intercept light oscillating in the resonant optical cavity and is operable to tunably change the mode frequencies of the at least one longitudinal mode of the resonant optical cavity. In another aspect, a resonant optical cavity is provided. The resonant optical cavity supports oscillation of light in at least one longitudinal mode having a respective mode frequency. Light in at least one longitudinal mode in the resonant optical cavity is amplified. The mode frequencies of the resonant optical cavity are changed. The light is transmission band-pass filtered.

1 . A frequency-tunable light source, comprising: 
 a resonant optical cavity supporting oscillation of light in at least one longitudinal mode having a respective mode frequency;    an optical gain medium disposed in the resonant optical cavity and s operable to amplify light;    an optical mode filter arranged to intercept light oscillating in the resonant optical cavity and having an optical transmission pass-band with a tunable center frequency; and    a mode frequency tuner arranged to intercept light oscillating in the resonant optical cavity and operable to tunably change the mode frequencies of the at least one longitudinal mode of the resonant optical cavity.    
   
   
       2 . The frequency-tunable light source of  claim 1 , wherein the pass band of the optical mode filter has a 3 dB bandwidth encompassing at most 10 of the longitudinal modes supported by the resonant optical cavity.  
   
   
       3 . The frequency-tunable light source of  claim 1 , wherein the optical mode filter comprises a tunable optical interference element.  
   
   
       4 . The frequency-tunable light source of  claim 3 , wherein the optical interference element comprises an etalon.  
   
   
       5 . The frequency-tunable light source of  claim 1 , wherein the mode frequency tuner comprises an acousto-optic device arranged to intercept light oscillating in the resonant optical cavity and operable to impose a Doppler shift on the mode frequencies of the at least one longitudinal mode of the resonant optical cavity.  
   
   
       6 . The frequency-tunable light source of  claim 5 , wherein the mode frequency tuner comprises a second acousto-optic device arranged to intercept light oscillating in the resonant optical cavity and operable to impose a second Doppler shift on the mode frequencies of the at least one longitudinal mode of the resonant optical cavity, wherein the first and second Doppler shifts are in opposite directions.  
   
   
       7 . The frequency-tunable light source of  claim 6 , wherein the first and second acousto-optic devices are selected from: acousto-optic deflectors; acousto-optic modulators; and acousto-optic tunable filters.  
   
   
       8 . The frequency-tunable light source of  claim 6 , further comprising a driver connected to the first and second acousto-optic devices.  
   
   
       9 . The frequency-tunable light source of  claim 8 , wherein the driver is configured to drive the first and second acousto-optic devices at different respective drive frequencies in one operational mode of the frequency-tunable light source.  
   
   
       10 . The frequency-tunable light source of  claim 8 , wherein the driver is configured to drive the first and second acousto-optic devices at substantially equal frequencies but with different relative phases in one operational mode of the frequency-tunable light source.  
   
   
       11 . The frequency-tunable light source of  claim 8 , wherein the driver is configured to vary the frequencies of the first and second drive signals in a manner substantially correcting deviation of light by the mode frequency tuner as a result of changing the mode frequencies of the longitudinal modes of the resonant optical cavity.  
   
   
       12 . The frequency-tunable light source of  claim 1 , wherein the resonant optical cavity is defined between a first reflector and a second reflector.  
   
   
       13 . The frequency-tunable light source of  claim 12 , wherein the first reflector comprises a facet of the optical gain medium.  
   
   
       14 . The frequency-tunable light source of  claim 12 , wherein the second reflector comprises a retroreflector.  
   
   
       15 . The frequency-tunable light source of  claim 1 , wherein the resonant optical cavity is a circulating optical cavity.  
   
   
       16 . A method of generating wavelength-tunable light, comprising: 
 providing a resonant optical cavity supporting oscillation of light in at least one longitudinal mode having a respective mode frequency;    amplifying light in at least one longitudinal mode in the resonant optical cavity;    changing the mode frequencies of the resonant optical cavity; and    transmission band-pass filtering the light.    
   
   
       17 . The method of  claim 16 , wherein the transmission band-pass filtering has a center frequency substantially corresponding to a target optical frequency of the light.  
   
   
       18 . The method of  claim 17 , further comprising tuning the center frequency of the optical transmission band-pass filtering to track the changing of the mode frequencies of the resonant optical cavity.  
   
   
       19 . The method of  claim 16 , wherein the optical transmission band-pass filtering has a 3 dB bandwidth encompassing at most 10 of the longitudinal modes of the resonant optical cavity.  
   
   
       20 . The method of  claim 16 , wherein changing the mode frequencies of the resonant optical cavity comprises imposing first and second Doppler shifts on the light in opposite directions.  
   
   
       21 . The method of  claim 20 , wherein changing the mode frequencies of the resonant optical cavity further comprises imposing the first and second Doppler shifts differing in magnitude by an amount selected to achieve a desired time-dependent variation in the frequency of the light.